This invention relates generally to storage tanks and more particularly to in-ground storage tanks and an improved method of installing them.
Storage tanks installed underground have been used to retain a wide range of materials. Large storage tanks require a significant excavation in order to install them underground. To properly place and position the tank within the excavation, and thereafter to ensure that the tank is evenly supported by the backfill subsequently added to the excavation, workers have had to enter the excavation. In the United States, OSHA has promulgated worker safety rules which require that the sidewalls of the excavation be sloped or that sheet piling be provided along the walls to reduce the likelihood that the walls will collapse on the workers in the excavation. The sloped walls required by OSHA standards increase the size of the excavation and the time and cost to make the excavation. Similar authorities around the world have also promulgated similar rules.
Notably, with an underground storage tank of generally circular cross sectional shape, the lower portion of the tank must be supported evenly along its entire length to prevent concentration of stresses or bending or failure of the tank. To do this with a conventional storage tank and conventional process of installing the tank, workers have to enter the excavation to shovel or otherwise distribute backfill evenly under the tank. Thus, the excavation must be provided with sheet piling or sloped walls to protect the workers against a cave-in.
An underground storage tank with backfill deflectors is provided to permit installation of the storage tank underground without requiring any workers to enter the excavation. The backfill deflectors are preferably elongate, and generally equal in length or longer than the storage tanks with which they are used and are installed on the bottom of the excavation on either side of the tank. The deflectors have walls which are sloped or inclined in a direction which tends to direct backfill dumped thereon underneath the storage tank. Desirably, the deflectors direct the backfill under the tank without requiring any of the workers to enter the excavation to shovel the backfill underneath the lower portion or haunches of the tank. After a sufficient level of backfill is introduced into the excavation and directed under the tank by the deflectors, the backfill is vibrated to achieve a compacted backfill under the tank which is sufficient to support the tank. Preferably, the backfill is vibrated with a concrete vibrator with a probe on a long cord or tether, and may be accomplished without any workers entering the excavation. Such a vibrator, commonly used to compact concrete in forms, will move the backfill into any voids in the backfill under the tank to provide an even support for the bottom of the tank along its entire length. The backfill may also be compacted with a probe delivering compressed air onto or into the backfill.
The deflectors may be separate from the storage tank, being initially installed in the excavation in spaced relation, with the tank then set between the deflectors. Alternatively and preferably, the deflectors may be carried by the storage tank at least during installation of the tank and may be movable from a retracted position for shipment to an extended position suitable to deflect backfill underneath the tank. In another form, a cradle or base may be positioned beneath the tank with a supporting surface preferably complimentary to the bottom surface of the tank and the deflectors may be carried by the base and used to deflect backfill against the base and underneath portions of the tank not supported by the base. In any form, the backfill deflectors promote the displacement of backfill underneath the tank and permit installation of the tank underground without requiring any workers to enter the excavation. Therefore, no sheet piling needs to be provided, the walls of the excavation do not need to be sloped and the size of the excavation can be minimized for the particular application to reduce the time and cost to install the tank.
Objects, features and advantages of this invention include providing backfill deflectors for an underground storage tank which reduces the size of an excavation needed to install the tank, drastically improves worker safety by eliminating the need for any workers to enter the excavation to install the tank, provides a uniformly compacted layer of backfill underneath the tank to evenly support the tank along its length, reduces the likelihood that the tank will bend or fail due to lack of support, permits the tank to be strapped down to reduce or eliminate buoyancy of the tank, eliminates the need for a concrete slab over the top of the installed tank or below the tank or dead man strip anchors alongside the tank to prevent floatation of the tank, reduces the time and cost to make the excavation, and is of relatively simple design and economical manufacture and assembly.